CHEYENNE, Wyo. (AP) — Sinclair Oil Corp. has agreed to pay a $3.8 million fine for two of its Wyoming oil refineries exceeding air pollution limits that had been established three years earlier in another settlement with the federal government, authorities announced Monday.

Sinclair also agreed to spend about $10.5 million on additional pollution control equipment and other measures at its refineries in Casper and east of Rawlins in the town of Sinclair, according to the Environmental Protection Agency.

Clint Ensign, senior vice president of Sinclair Oil, said the company has been working on the air pollution issues at the Wyoming operations.

"Sinclair Oil Corp. has worked in good faith with the government to reach agreement on the consent decree and the company has resolved, or is in the process of resolving, items of concern noted in that document," Ensign said in a statement.

The EPA said the refineries failed to comply with nitrogen oxide and sulfur dioxide emission limits set in a 2008 settlement. Sinclair had paid a $2.45 million penalty and agreed to invest up to $72 million in new and improved air pollution controls at its two Wyoming plants and another in Oklahoma.

"Parties who enter into consent decrees with the United States must adhere to their obligations, and failure to comply will result in further penalties," Ignacia S. Moreno, assistant attorney general for the U.S. Justice Department, said in a statement.

Cynthia Giles, assistant administrator for EPA's enforcement office, said the settlement holds Sinclair Oil accountable and ensures cleaner air in Wyoming.

According to the EPA, the new settlement requires Sinclair Oil to reduce nitrogen oxides emissions from the two Wyoming operations by about 24 million tons a year and sulfur dioxide by about 385 million tons a year. The two pollutants will be reduced by installing new and improved pollution control equipment at the plants.

In addition, the company must pave a road and reduce fuel oil burning at its Casper refinery to cut down on dust and exhaust.

EPA says the proposed settlement is subject to a 30-day public comment period and final court approval.